Secondary recovery of hydrocarbons involves the use of an injection well into which liquid or gas is injected in order to cause the hydrocarbons to migrate away from the injection well and toward a production well. There are many wells in the United States that are undergoing secondary recovery, and some day these same wells will be subjected to tertiary recovery. It is estimated that after primary recovery has taken place more than 80 percent of the hydrocarbons are left downhole. Accordingly, it is economically expedient to inject a gas, such as CO.sub.2 or flue gases; or a liquid, such as salt water, into the injection well and in a predetermined pattern of wells, thereby causing some of the remaining hydrocarbons to be forced to migrate toward the production well.
The pressure at the wellhead of the injection well is considerable, and a lot of money and time must be invested in order to achieve the desired downhole formation injection pressure and for the system to reach equilibrium. A substantial amount of this injected material is lost whenever the well is bled down.
Occasionally a tubing string of an injection well must be pulled from its casing, and it has heretofore been necessary to bleed the well down until the hydrostatic head on the well causes the wellhead pressure to become atmospheric or less, so that the tubing string can be safely pulled without the danger of causing a blowout.
Accordingly, bleeding down the well is extremely expensive and represents substantial loss in money and time, as well as upsetting the injection pattern, causing the migration of the fluid to deviate from the desired path of travel.
The present invention provides method and apparatus for hanging and sealing a tubing string in a high pressure wellbore. The present invention provides apparatus which can advantageously be used to enable the tubing string of an injection well to be pulled under high pressure, thereby avoiding the necessity of bleeding down the well prior to invention allows the removal of the production equipment and the installation of a snubbing unit to be done prior to opening the well bore into the snubbing apparatus. This enables the snubbing apparatus to be used in pulling the tubing string and subsequently used to run a string back into the wellbore; and, thereafter to enable the production equipment to be replaced so that the well is back in operation with no appreciable loss of downhole pressure.